This invention relates to a multi-piece solid golf ball comprising a rubbery elastic solid core and a resin cover of a plurality of layers enclosing the solid core, and more particularly, to such a multi-piece solid golf ball having a resin layer of at least three layers which is improved in flight distance performance and controllability.
One of known solid golf balls has the structure in which a rubbery elastic solid core is enclosed with a cover of relatively hard ionomer resin characterized by good external damage prevention such as cut resistance and abrasion resistance.
The solid golf ball of this structure has improved flight distance performance, but gives a hard feel when hit, about which skilled golfers such as professional golfers complain. Attempts have been made to moderate the feel by constructing the resin cover from a plurality of layers including an inner layer and an outer layer, and endowing the inner layer with softness or increasing the gage of the inner layer.
However, merely making the cover inner layer softer or thicker gives rise to other problems that the ball receives more spin when hit with a small loft club such as a driver, the ball becomes less rebound and thus travels shorter, and the ball is likely to sky when hit with an iron club against the wind.
Therefore, an object of the invention is to provide a high-performance multi-piece solid golf ball comprising a rubbery elastic solid core and a resin cover of at least three layers, which ball prevents any undesired increase of spin upon driver shots without detracting from the rebound of the ball, has good flight performance, receives enough spin to facilitate control on short iron shots, and has durability and a pleasant feel when hit.
According to the invention, there is provided a multi-piece solid golf ball comprising a rubbery elastic solid core and a resin cover enclosing the solid core. The cover comprises at least three layers including an inner layer disposed adjacent to the solid core, an outer layer disposed radially outside the inner layer and provided on its outer surface with a multiplicity of dimples, and an intermediate layer between the inner layer and the outer layer. The solid core has a hardness corresponding to a deflection of at least 1.6 mm under an applied load of 294 N (30 kgf). The cover inner layer has a Shore D hardness of at least 55. The cover outer layer has a Shore D hardness of 40 to 55. The cover intermediate layer has a Shore D hardness X of 8 to 50 and a gage Y of up to 1.2 mm, wherein X and Y satisfy the relationship: X/Yxe2x89xa735. Desirably the Shore D hardness of the cover layers is in the order of inner layerxe2x89xa7outer layerxe2x89xa7intermediate layer.
In a preferred embodiment, the dimples are circular as viewed in plane, and the sum of dimple trajectory volumes each given as the volume of a dimple multiplied by the square root of a dimple diameter is in the range of 530 to 750.
Preferably, the cover inner layer is formed mainly of an ionomer resin or a resin blend of an ionomer resin with a polyolefin elastomer.
Preferably, the cover intermediate layer is formed mainly of a polyester elastomer, polyurethane elastomer, polyolefin elastomer, polyamide elastomer, ionomer resin or a mixture thereof and has a gage of 0.1 to 1.2 mm.
Preferably, the cover outer layer is formed mainly of a thermoplastic polyurethane elastomer, thermosetting polyurethane elastomer, polyester elastomer or a mixture thereof, and more preferably, it is formed mainly of a thermoplastic polyurethane elastomer obtained using an aromatic or aliphatic diisocyanate, or the reaction product of a thermoplastic polyurethane elastomer with an isocyanate compound.
Preferably, an adhesive layer intervenes between two adjacent layers of the cover.
In a multi-piece solid golf ball comprising a rubbery elastic solid core and a resin cover of at least three layers and having a multiplicity of dimples on the ball surface, the hardness and gage of the cover layers are properly combined whereby any undesired increase of spin upon full driver shots is restrained without detracting from the rebound of the ball. The sum of dimple trajectory volumes VT each given as the volume of a dimple multiplied by the square root of a dimple diameter is adjusted to an optimum range, whereby the ball follows a rather low trajectory which is further stretched near its fall. These factors cooperate to produce a high-performance multi-piece solid golf ball having advantages including minimized wind influence, improved flight performance, and an increased run upon shots with a driver, and good spin performance upon approach shots with a short iron.